(China Focus Face to Face) What is the difficulty of the "Fifth" lunar exploration?

What is the use of "digging" the moon?

  China News Service, Beijing, November 24th, title: What is the difficulty of the "Fifth" lunar exploration?

What is the use of "digging" the moon?

  ——Interview with Li Qing, deputy chief designer of the Chang'e-5 probe of the Fifth Academy of China Aerospace Science and Technology Corporation

  Author Zhang Su Guo Chaokai

  At 4:30 on November 24th, the Long March 5 Yaowu carrier rocket successfully launched the lunar exploration project Chang'e 5 probe, and successfully sent the probe into the scheduled orbit, starting China's first return journey for sampling extraterrestrial objects.

  This is the final battle of China's lunar exploration project in the three steps of "circumnavigation, landing, and return", and it is one of the most complex and difficult tasks in China's aerospace industry so far.

What is the difficulty of "Changwu" lunar exploration?

What is the use of "digging" the moon?

On the 24th, Li Qing, the deputy chief designer of the Chang'e-5 probe of the Fifth Academy of China Aerospace Science and Technology Corporation, accepted an exclusive interview with China News Agency "Focus on China" for an authoritative interpretation.

  Excerpts from the interview are as follows:

China News Agency reporter: Why is the launch window selected in the early morning? What conditions should the best launch time meet?

  Li Qing: The best launch time depends on the mission design.

The main task of the Chang'e-5 probe is to complete the lunar surface sampling.

To ensure the best measurement and control state during the sampling process, we hope to complete it in the middle of the night on the earth and the day on the moon.

This time is also equivalent to what we call the full moon state. The full moon has the best observation conditions for the moon, as well as the best measurement and control conditions. Subject to these conditions, we have calculated the orbital calculation and found that the best launch time is in the early morning. Around 4:30.

At 4:30 on November 24, China successfully launched the Lunar Exploration Project Chang'e-5 probe using the Long March 5 Yaowu carrier rocket at the Wenchang Space Launch Site.

Photo by Luo Yunfei

China News Agency reporter: From Chang'e-1 to Chang'e-5, please take us to review the history of China's lunar exploration.

  Li Qing: China's lunar exploration project follows a three-step strategy of "circumnavigating, descending, and returning" and has so far successfully executed five missions.

  Chang'e-1 was launched at the Xichang Satellite Launch Center in October 2007. After completing the scheduled orbital detection mission, it successfully controlled its collision with the moon in March 2009.

  As the pilot mission of the second phase of the project, Chang'e-2 was successfully launched in October 2010. After high-resolution imaging of the Hongwan area where Chang'e-3 was about to land, it began to expand its mission in April 2011 and completed its entry into the sun and earth. The technical test of Lagrangian L2 orbit, followed by flying over the asteroid Tutatis and sending back photos, has become China's farthest probe from the earth, and it has also opened a precedent for China's multi-target deep space exploration.

  The Chang'e-3 probe is composed of a lander and a patrol device. It was successfully launched in December 2013 and landed safely in the Hongwan area on the front of the moon. After landing, the patrol device and the lander were separated and completed the scheduled lunar surface detection tasks.

  The Chang'e-5 flight tester is mainly used to verify the semi-ballistic jump reentry and return technology. It was successfully launched in October 2014. After the earth-moon transfer, the moon turn near the moon, and the moon-earth transfer, the returner and the service module were separated and carried out. Re-enter and return, and finally successfully landed in the planned area of ​​Siziwang Banner, Inner Mongolia.

  Chang'e-4 has made adaptive improvements on the basis of Chang'e-3, selected the back of the moon to carry out landing and patrol detection missions, and launched the relay star "Magpie Bridge" to solve the communication problem. It successfully landed on the south pole of the back of the moon in January 2019 -The Aitken Basin, the world's first spacecraft to achieve soft landing patrol detection on the back of the moon, is still in normal operation.

  The Chang'e-5 probe (on mission) consists of an orbiter, a returner, a lander and an ascender.

According to the latest news, it was launched by the Long March 5 Yaowu carrier rocket at about 4:30 am today, and it has successfully entered the Earth-Moon transfer orbit.

Li Qing, deputy chief designer of the Chang'e-5 probe of the Fifth Academy of China Aerospace Science and Technology Corporation, accepted an exclusive interview with China News Service.

Photo by China News Agency reporter Zhang Xinglong

China News Agency reporter: Can you give us a detailed introduction to the mission of Chang'e 5?

  Li Qing: The mission of China's Chang'e-5 probe is to realize automatic sampling and return of the lunar surface, collect about 2 kilograms of lunar samples and return them, and carry out ground analysis and research on lunar samples.

  The entire mission flight process is divided into 11 stages, with a total flight time of about 23 days.

  The first stage is launching into orbit.

The probe was launched by the Long March 5 carrier rocket and entered the Earth-Moon transfer orbit after separation.

This stage has been completed today.

  The second stage is the earth-moon transfer section.

The probe flew along the Earth-Moon transfer orbit for about 5 days and reached the near-moon point at an orbital altitude of about 200 kilometers. During this period, it will undergo 1 to 3 midway corrections.

  The third stage is the braking section of the recent month, (ie) "brake".

The probe implements a near-moon brake near the near-moon point and enters an elliptical orbit around the moon with a height of 200 kilometers at the near-moon point; after three rounds of the elliptical orbit, it implements a second near-moon brake and enters the average altitude A 200-kilometer orbit around the moon.

The flight time during braking in recent months is about 1 day.

  The fourth stage is the circumlunar flight.

After the probe flew in a circular orbit around the moon for about 4 times, the landing ascending assembly and the orbiting assembly were separated, and the orbiting assembly continued to fly around the moon. The landing ascending assembly was carried out after orbiting the orbit for about 12 times. Two down orbit changes, entering an elliptical orbit about 15 kilometers from the near moon point and 200 kilometers from the far moon point.

  The fifth stage is the landing stage.

After the landing ascent assembly continues to run on the elliptical orbit around the moon for about 10 laps, it chooses an opportunity to perform a landing descent, and performs a soft landing on a predetermined area on the lunar surface. The landing and descent process takes about 15 minutes.

  The sixth stage is the lunar working section.

After the landing ascent assembly landed, two sampling methods, drilling and surface sampling, were used to complete the sampling and packaging of the lunar soil; at the same time, the payload carried out in-position detection; after the sampling, the ascender was positioned on the lunar surface to complete the ascender Ready for takeoff.

The working time on the moon is about 2 days.

  The seventh stage is the ascending phase of the moon.

After the lunar surface work is completed, the ascender uses the lander as a platform to take off. After vertical ascent, posture adjustment, and orbit incidence, it enters the ascending target orbit of 15 kilometers near the moon and 180 kilometers at the far moon. The flight time is about 6 minutes.

  The eighth stage is the rendezvous and docking and sample transfer section.

After the ascender enters the target orbit, through four orbital maneuvers, it is finally guided to a circular orbit around the moon with a height of 210 kilometers.

The remote guidance time of the ascender is about 2 days.

When the ascender is located about 50 kilometers in front of the orbit-return assembly and about 10 kilometers above it, it begins to enter the short-range autonomous control section.

The orbit-back assembly is the active aircraft, and the ascender is the target aircraft. The initial conditions required for docking and docking are established, and the docking starts.

After the orbiter docking mechanism captures and locks the ascender, the sample transfer mechanism starts to move and transfers the sample container in the ascender to the interior of the returner to complete the sample transfer operation; then the orbiter-back assembly selects the opportunity to separate from the ascender and the docking cabin.

  The ninth stage is the waiting period around the moon.

The orbit-back assembly stays in the orbit around the moon for 5 to 7 days, waiting for the lunar-ground transfer window.

  The tenth stage is the lunar land transfer section.

After the orbit-back assembly arrives at the lunar-earth transfer window, it enters the lunar-earth transfer orbit by implementing two orbital maneuvers.

The lunar-ground transfer flight time is about 4 to 5 days, during which 1 to 3 midway corrections will be implemented to meet the requirements of the returner's re-entry point parameters.

  The eleventh stage is to re-enter the recovery section.

When the height of the orbit-return assembly is about 5000 kilometers from the earth's surface, the orbiter and the returner are unlocked and separated.

After the separation, the orbiter made an evasive maneuver. The returner returned to the earth in a semi-ballistic jump reentry mode, opened its parachute at an altitude of 10 kilometers, and finally landed on the Siziwang Banner landing site in Inner Mongolia.

Li Qing, deputy chief designer of the Chang'e-5 probe of the Fifth Academy of China Aerospace Science and Technology Corporation, accepted an exclusive interview with China News Service.

Photo by China News Agency reporter Sheng Jiapeng

China News Agency reporter: In layman's terms, this mission is to "grab a handful of soil and return to the earth."

What kind of "soil" is "this handful of soil"?

Why choose to bring back such a sample?

How will it help future scientific research?

  Li Qing: The Chang'e-5 detector has designed two sampling methods, namely drilling sampling and table sampling.

Drilling sampling is to use a drill pipe of about 2 meters (long) into the lunar surface to collect a sample of about 0.5 kg at a depth of two meters.

Table sampling is to use a robotic arm for multi-point sampling. The sampling area includes flat ground, impact craters, bumps, and small rocks. These samples can be used as sampling samples. These samples have different distributions, different geological characteristics, and different evolutionary history. Improve the value of scientific research.

After drilling sampling and table sampling sampling, they are packaged separately, and then the sample container is sealed to ensure that the sample is not polluted by the external environment during the return process.

China News Agency reporter: This mission is known as one of the most complex and difficult missions in the aerospace field so far. How do you define "the most complex and difficult"?

What is the difficulty of the task?

  Li Qing: The technical difficulties of the Chang'e-5 probe mission are mainly manifested in the orbit design, lunar surface sampling and packaging, lunar surface take-off and rise, lunar orbital rendezvous and docking, and sample transfer.

  The first is the complicated design of the lunar orbit.

Because there are many flight stages of the Chang'e-5 probe, the orbital schemes of each stage are closely coupled, involving multiple restrictions on measurement and control, carrying and landing sites, and many constraints. The flight process also involves lunar take-off, orbital rendezvous and docking, lunar-earth orbit, etc. The new flight phase was not involved in the previous "around" and "landing" missions.

The flight process is complex and the orbit design is difficult. In the nominal orbit design scheme, various plans need to be formulated under the condition of limited propellant resources. This is also a new challenge to the orbit design.

  The second is the lunar surface sampling and packaging technology, which is a brand-new technology and one of the core links of the Chang'e 5 lunar unmanned sampling and return mission.

This task uses the combination of drilling and table fetching, multi-point sampling, and the sampling device is newly developed. The technology is new and difficult. It needs to consider various constraints such as flight mission and detector measurement and control, lighting conditions, power supply, and thermal control. During this period, I was faced with the working environment of continuous high temperature on the lunar surface, and at the same time, the sampling task was tight in time sequence, many mechanism actions and many uncertain factors.

  The third is that it is difficult to verify the lunar takeoff and rise.

The lunar take-off system composed of ascenders, landers and the lunar surface, its initial state is derived from the conditions of the landing ascendant's landing on the lunar surface, the landing attitude and azimuth, etc. The initial conditions for the lunar take-off cannot be like that of a carrier rocket Like missiles, ground personnel complete the measurement, adjustment and confirmation on the ground, and must rely on autonomous positioning and attitude determination to determine the initial state of takeoff.

In the face of oblique launch, it is necessary to clarify the various factors of takeoff stability and their coupling effects, and rely on accurate attitude determination capabilities to complete aerial alignment to achieve accurate orbit.

Different from the plume environment faced by conventional spacecraft, the ignition of the ascender engine in a confined space has a very complicated plume force thermal effect, which needs to be verified by a large number of ground simulations and experiments.

  Fourth, the lunar orbital rendezvous and docking and sample transfer require high autonomy.

Unlike the low-Earth orbit rendezvous and docking, the Chang'e 5 lunar orbital rendezvous and docking is not supported by satellite navigation signals, and the autonomy of the docking and sample transfer process is very demanding.

At the same time, during the lunar rendezvous and docking process, the ground measurement and control support capability is limited, and the docking mechanism is limited by the size, and the docking accuracy is relatively high.

The docking and sample transfer mechanism of Chang'e-5 detector must meet the relevant requirements of sample transfer while ensuring docking accuracy.

The integrated design of the docking mechanism and the sample transfer mechanism is also a difficult point in the research of this technology.

China News Agency reporter: "Returning" is a key step in "winding, falling, and returning". What scientific goals do we hope to achieve?

  Li Qing: As the three-step final battle of the Chinese lunar exploration project, the mission of Chang'e-5 is of great significance, far-reaching influence and attracting worldwide attention.

In the three-step target, "circle" is the completion of China's first lunar orbit detection mission, and "fall" is the completion of China's first lunar soft landing and inspection mission.

The key step of the final “return” will be the realization of China’s first lunar unmanned sampling and return mission, including multiple firsts: the first automatic sampling and packaging of the lunar surface, the first lunar take-off and ascent, the first lunar orbital rendezvous and docking, and the first lunar rendezvous high-speed (In) Return to Earth, storage, analysis and research of the first self-collected lunar sample.

  The scientific goals of the Chang'e-5 mission are mainly to carry out the landform area detection and geological background survey, obtain the on-site analysis data related to the lunar samples, establish the connection between the on-site exploration data and the laboratory analysis data; carry out the system of the lunar samples , Long-term laboratory research to analyze the structure, physical properties, and material composition of the lunar soil, and deepen the research on the origin and evolution of the moon.

At 4:30 on November 24, China successfully launched the Lunar Exploration Project Chang'e-5 probe using the Long March 5 Yaowu carrier rocket at the Wenchang Space Launch Site.

Photo by Luo Yunfei

Reporter from China News Service: You mentioned a number of firsts, and you also mentioned that the three steps of "winding, falling, and returning" have far-reaching impact.

Will this have a major breakthrough in helping us understand the moon?

  Li Qing: The completion of the three-step lunar exploration indicates that China has mastered a comprehensive lunar unmanned exploration technology.

Through the research results of the lunar exploration project, Chinese scientists have greatly improved the global, integral and comprehensive understanding of the lunar topography and geological structure, material composition, lunar soil characteristics, and lunar surface environment, enabling China to master the first The lunar exploration data of the hand provides a scientific basis for the subsequent lunar exploration project and the site selection and construction of the lunar scientific research station.

Reporter from China News Agency: Another "net celebrity" in the lunar exploration project is the Yutu 2 lunar rover. It is understood that it has completed its autonomous wake-up and started a new round of moon and day work.

Can you tell me the difference between Yutu 2 and Chang'e 5?

  Li Qing: The "Yutu" lunar rover actually refers to the patrol device carried by the "Chang'e" lander.

The "Yutu-1" lunar rover is the patrol device of the Chang'e-3 probe, and the "Yutu-2" lunar rover is the patrol device of the Chang'e-4 probe, so they are all part of the Chang'e probe.

  In addition to ensuring the safe landing of the entire probe, the "Chang'e" lander also has an in-situ detection function. Through long-term in-situ detection, more detailed detection data and time history near the landing area can be obtained.

The "Yutu" lunar rover has a mobile device, which is mainly used for patrol and detection, which can greatly expand the range of lunar surface detection.

These two detection methods complement and combine with each other, which is beneficial to improve the efficiency of detection.

China News Service: Relying on the lunar scientific research data we have obtained, do you think it is possible to build our lunar home like in modern science fiction films?

  Li Qing: The myths and legends of Chang'e flying to the moon entrusted the ancient Chinese people's beautiful fantasy of the moon.

Based on the results of the current lunar exploration process and the future lunar exploration plan, the establishment of a lunar home—that is, the establishment of a comprehensive lunar research station that supports the survival of long-term personnel, or the moon village—has actually been put on the planning agenda. Technically, although there are still many key technologies to be broken through, there should not be too much science fiction.

This is also the general trend of the development of human aerospace industry.

  But what I want to emphasize is that it is consistent for a long time.

With the continuous support of the policy, the long-term peaceful domestic and international environment, the long-term good international cooperation atmosphere, and the unremitting efforts of all aerospace workers, this genius is expected to come soon.